This invention relates to a method for the remote tracking in real-time of the spatial coordinates of a stationary or moving object in three dimensional space.
Interferometry methods for the location of an emitter source are known which require the knowledge of several parameters such as, waveform modulation, emitter signal angle of arrival or time of arrival, or measurements of angular rates between the emitter source and the measurements site. It is known in the art to use interferometry and tracking systems which utilized amplitude and phase comparison relationships to determine either the direction or spatial coordinates of a remote object relative to that of the receiver or an arbitrary reference. Conventional direction and range tracking systems typically utilize planar propagating electromagnetic waves. Conventional planar wave propagating systems become less accurate as the distance between the object under observation and the receiver decreases. For close range applications (which are generally considered to be where the location of the object relative to the sensory array is less than one hundred times the largest distance between sensor elements) the margin of error associated with conventional techniques is often unacceptable. Also, additional expense is required if spatial coordinates must be determined in addition to direction finding capability.
In order to obtain the actual coordinates of the emitter location using conventional plane wave propagating techniques, either triangulation methods, or range and direction detection methods are commonly used. Often, unacceptable system costs and limitations in tracking may result from additional measurement time requirements in such systems. If three dimensional rather than two dimensional tracking is required, time and cost requirements can be amplified even further. Due to the relatively large physical dimensions of interferometer sensors and triangulation baseline, serious limitations in performance and application often occur with the use of the planar wave interferometry. When the distance separating the receiver and the object decreases to a point where the accuracy of the tracking measurements is degraded to an unacceptable state, a different technique must be considered.
Optical and sub-optical frequency electromagnetic (EM) wave energies as well as acoustical wave energies, have been most commonly used. Systems such as optical interferometers utilized for direction tracking require mechanical servo mechanisms and are not fault tolerant, in that realignment and calculation of the target coordinates after power failure is required.
U.S. Pat. No. 4,788,548 of Hammerquist discloses a passive radar ranging system capable of determining the two dimensional range of an emitter source using four co-linear antenna receiver elements. However, the technique of Hammerquist is limited to two dimensional range determination.
It is an object of this invention to provide a method for the fault tolerant, continuous, real-time, high resolution determination of three dimensional spatial coordinates of objects.
It is another object of this invention to provide a method for determining in real-time close range three dimensional coordinates of objects using a broad spectrum of frequencies.
It is still another object of this invention to provide a method for determining the three dimensional full or half space coordinates of an object when the waveform is unmodulated, randomly modulated, or pulsed.
It is still a further object of this invention to provide a method for determining spatial coordinates or tracking of an object at low frequencies to penetrate poor climate and atmospheric conditions.
Additional objects, advantages and novel features of the invention will become apparent to those skilled in the art upon examination of the following and by practice of the invention.